We are given two logarithm problems to solve for $x$. Problem 5: Find $x$ if $\log_{10}(2x+1) - \log_{10}(3x-1) = 1$. Problem 6: Find $x$ if $\log_{10}5 + \log_{10}(x+2) - \log_{10}(x-1) = 2$.

AlgebraLogarithmsEquationsSolving EquationsLogarithmic EquationsAlgebraic Manipulation
2025/3/17

1. Problem Description

We are given two logarithm problems to solve for xx.
Problem 5: Find xx if log10(2x+1)log10(3x1)=1\log_{10}(2x+1) - \log_{10}(3x-1) = 1.
Problem 6: Find xx if log105+log10(x+2)log10(x1)=2\log_{10}5 + \log_{10}(x+2) - \log_{10}(x-1) = 2.

2. Solution Steps

Problem 5:
log10(2x+1)log10(3x1)=1\log_{10}(2x+1) - \log_{10}(3x-1) = 1
Using the logarithm property loga(b)loga(c)=loga(bc)\log_a(b) - \log_a(c) = \log_a(\frac{b}{c}), we have:
log10(2x+13x1)=1\log_{10}(\frac{2x+1}{3x-1}) = 1
Convert the logarithmic equation to an exponential equation using loga(b)=c    ac=blog_a(b)=c \implies a^c = b:
2x+13x1=101\frac{2x+1}{3x-1} = 10^1
2x+13x1=10\frac{2x+1}{3x-1} = 10
Multiply both sides by (3x1)(3x-1):
2x+1=10(3x1)2x+1 = 10(3x-1)
2x+1=30x102x+1 = 30x - 10
Subtract 2x2x from both sides:
1=28x101 = 28x - 10
Add 1010 to both sides:
11=28x11 = 28x
Divide both sides by 2828:
x=1128x = \frac{11}{28}
We need to check if this value of xx is valid by plugging it back into the original equation.
2x+1=2(1128)+1=1114+1=2514>02x+1 = 2(\frac{11}{28}) + 1 = \frac{11}{14} + 1 = \frac{25}{14} > 0
3x1=3(1128)1=33281=528>03x-1 = 3(\frac{11}{28}) - 1 = \frac{33}{28} - 1 = \frac{5}{28} > 0
Since both 2x+12x+1 and 3x13x-1 are positive for x=1128x = \frac{11}{28}, this solution is valid.
Problem 6:
log105+log10(x+2)log10(x1)=2\log_{10}5 + \log_{10}(x+2) - \log_{10}(x-1) = 2
Using the logarithm property loga(b)+loga(c)=loga(bc)\log_a(b) + \log_a(c) = \log_a(bc) and loga(b)loga(c)=loga(bc)\log_a(b) - \log_a(c) = \log_a(\frac{b}{c}), we have:
log10(5(x+2)x1)=2\log_{10}(\frac{5(x+2)}{x-1}) = 2
Convert the logarithmic equation to an exponential equation using loga(b)=c    ac=blog_a(b)=c \implies a^c = b:
5(x+2)x1=102\frac{5(x+2)}{x-1} = 10^2
5x+10x1=100\frac{5x+10}{x-1} = 100
Multiply both sides by (x1)(x-1):
5x+10=100(x1)5x+10 = 100(x-1)
5x+10=100x1005x+10 = 100x - 100
Subtract 5x5x from both sides:
10=95x10010 = 95x - 100
Add 100100 to both sides:
110=95x110 = 95x
Divide both sides by 9595:
x=11095=2219x = \frac{110}{95} = \frac{22}{19}
We need to check if this value of xx is valid by plugging it back into the original equation.
x+2=2219+2=2219+3819=6019>0x+2 = \frac{22}{19} + 2 = \frac{22}{19} + \frac{38}{19} = \frac{60}{19} > 0
x1=22191=22191919=319>0x-1 = \frac{22}{19} - 1 = \frac{22}{19} - \frac{19}{19} = \frac{3}{19} > 0
Since both x+2x+2 and x1x-1 are positive for x=2219x = \frac{22}{19}, this solution is valid.

3. Final Answer

For problem 5: x=1128x = \frac{11}{28}
For problem 6: x=2219x = \frac{22}{19}

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